1. Technical Field
The present invention relates to a method for setting a transfer mode in a line interface device, and more particularly to a method for setting a transfer mode in a line interface device for supporting at least two modes.
2. Related Art
Typically, in order to establish communication between systems, one system must use the same data transmission method as a counterpart system in transmitting data to the counterpart system. For this purpose, each system contains a line interface device for data transmission/reception. Such a line interface device is composed of a single hardware unit such as a local area network (LAN) card, a line interface card, a digital service unit (DSU), and a channel service unit (CSU). The above hardware units support at least one line interface mode.
In the meantime, typical systems perform signal transmission/reception based on digital signals. A specific signal grade (Digital Signal X) is used as a term for a successive standard digital transmission rate or level. A transmission rate of 64 kilobits per second (Kbps) equal to a bandwidth for a single phone voice channel is used as a basic rate digital signal 0 (DS0). A T-carrier system widely used in North America and an E-carrier system widely used in Europe are all operated using a basic multiple of digital signal (DS) series (i.e., DS0, DS1, DS2, . . . , DSn).
The DS series will hereinafter be described in detail. The DS series are based on the digital signal X. The DS1 used as a signal of a T-1 carrier transmits 24 DS0 signals using a PCM (Pulse Code Modulation) method and a TDM (Time Division Multiplexing) modulation method. The DS2 multiplexes four DS1 signals at the same time, and transmits the multiplexed four DS1 signals at a rate of 6.312 megabits per second (Mbps). The DS3 used as a signal of a T-3 carrier is 28 times faster than the DS1, namely, it has a transfer rate of 44.736 Mbps.
European digital transmission format of E-1 contains 32 channels having a rate of 64 Kbps in such a way that data can be transmitted at a rate of 2.048 Mbps. E-1 carrier has a higher data transmission rate than the T-1 carrier, because it adapts all eight bits of its own channel to encode signals in a different way from the T-1 carrier. The E-1 carrier and the T-1 carrier may be interconnected for international communications. In more detail, a voice signal is sampled 8,000 times per second in a T-1 carrier system, and each sample is digitalized in 8-bit word. This digitalized sample signal is digitalized in 24 channels at the same time, and thereby a 192-bit frame is transmitted 8,000 times per second. In addition, since each frame is distinguished from other frames by a single bit, each frame is composed of 193 bits. Therefore, a transfer rate of the T-1 carrier can be calculated by the following Equation 1.192 bits/frame×8,000 frames+8,000 framing Bits   [Equation 1]
Based on the Equation 1, a transfer rate of the T-1 carrier becomes 1.544 Mbps. According to such a T-1 transfer mode using the transfer rate of the Equation 1, twelve DS1 frames produce a SP (Super Frame), and twenty-four DS1 frames produce an ESF (Extended Super Frame). The T-1 transfer mode performs data transmission using an AMI (Alternate Mark Inversion) or B8ZS (Bipolar with Eight Zero Substitution) line coding method. An E-1 transfer mode performs data transmission using a HDB3 (High Density Bipolar Three) method. A T-3 transfer mode performs data transmission using a B3ZS (Bipolar with Three Zero Substitution) line coding method according to a M23 multiplex application frame format or C-bit parity application frame format. Also, an E-3 transfer mode uses a HDB3 line coding method.
As described above, the aforesaid transfer modes are different in a line coding method. Therefore, in the case where a line interface device supports at least two transfer modes among the aforesaid transfer modes, an appropriate mode should be set in the line interface device. Such a transfer mode setup method has a disadvantage in that a system operator must manually set an appropriate transfer mode using a management system in case of using a transmission device or similar systems like this transmission device. In other words, the system operator must manually determine or select a transfer mode of a line interface device in a management system to establish communication with outside devices. Such disadvantageous transfer mode setup should be applied to all the systems having a line interface device for supporting at least two modes in a PC (personal computer) or transmission system, etc. In conclusion, a user or a system operator must inevitably determine a transfer mode in case of rebooting or initially setting up a system.